Extractor for screws and the like



June 1932. .7 N. RANDALL ET AL 1,363,045

EXTRACTOR FOR SCREWS AND THE LIKE Filed July 3., 1931 INVENTORS. Harman Panda I! M I BY James EJZZ/arai ATTORNEYS.

Patented June 14, 1932 UNITED STATES PATENT OFFICE NORMAN RANDALL, OF CLEVELAND, AND JAMES B. DILLA-RD, OF CLEVELAND HEIGHTS, OHIO, ASSIGNORS TO THE CLEVELAND TWIST DRILL COMPANY, OF CLEVELAND, OHIO, A CORPGRATION OF OHIO EXTRACTOR FOR- SCREWS AND THE LIKE Applic'ation filed July 3,1931. Serial No. 548,546.

This invention relates to extractors for threaded metal parts and has more particular reference to tools employed for removing'parts'of pipes, screws, 'etc., which have been twisted or broken off, leaving a portion threaded into an aperture without a projection which will permit the part to be removed by ordinary tools- Extracting devices of the above described character usually consist of an'operating portion which is provided with helically disposed ribs'or lands and intermediate flutes or grooves, a hole'being drilled in the broken H article and the tool forced-thereinto. The

' tool is then rotated in the direction which will extract the threaded article. O'n'e objection to tools of this type is that there is a'tendency to expand the hole intowhich'theextracting tool is inserted and thus force'th'e thread to on such article into tighter engagement with the aperture from which it is desired to eX- tract it. It isthe intent of the present invention to provide an extracting tool which gives a better turning moment on the object to be removed, and which also overcomes this expanding tendency. I

It is, accord'ngly, an object of the present invention to provide'an extracting tool which secures a better turning moment on the piece to be removed and which will not unduly eX-' pand the articlewhich is to be removed. A

further object of the invention is to provide an extracting tool operating on an improved principle and more efiicient in use than those heretofore-known. To the accomplishment of the foregoing and. related ends, said invention, then, consists ofthe means hereinafter fully described and particularly pointed out in the claims.

The annexed drawing and the following description set forth in detail certain mechanism embodying the invention, such disclosed means constituting, however, butone of various mechanical formsin which the principle of the invention may be used.

In said annexed drawing:

Fig. 1 is 'anfelevation of one modification of the improved extractor illustrating the manner in which it is used to remove a broken screw; Fig. 2 is a transverse horizontal section taken through the operating portion of the modification shown in Fig. 1; Fig. 3 is an elevation of another modification of the improved extractor; Fig.4 is a trans Verse horizontal section taken through the modification shown in Fig. 3; and Fig. 5 isa partial sectional elevation illustrating the use of the tool shown in Fig. 3 for removing a brokenthreaded pipe.

7 Referring to Fig. 1, the modification there shown consists of a body 6 having a squared end 7 or other device, for the application of turning means and a tapered operating portion 8. The operating portion 8 is provided with helically disposed lands or ribs 9 and intermediate grooves or flutes 11, these grooves running off into the body of the tool. As may be seen by reference to Fig. 2, the lands or ribs 9 are prepared with gripping edges and the forward face 12 of the rib is practically radially disposed. The tool may also be made up with this surface inclined toward the work, the land or rib having in such instance an overhanging contour in crosssection, or having what is known to the tool maker as a positive rake. An extracting tool formed with gripping edges of this character readily bites into the walls of a hole 18 previously drilled into the piece to be extracted, such as the screw 1 1 shown in Fig. 1.

The modification of the invention shown in Figs; 3, 4 and 5, consists of a body 15 having a square end 16 and an operating portion port the gripping edges 21 and prevent the lands from penetrating too deeply and expanding the hole. The manner of using this modification is similar to that of using the modification shown in Fig. 1, there being illustrated in Fig. 5 the application of the extracting tool to a piece of broken-off threaded pipe 23. Of course, it will be understood that either tool may be used for extracting either screws or threaded pipe or similar broken off parts.

The new extracting tool described above is intended to be used in the extraction of broken oif parts in the customary manner, that is, a hole is first bored into the screw which is to be extracted and the extractor inserted until the lands or ribs engage the sides of the hole. A wrench, bit brace, or other turning tool may then be applied to the extractor at the squared end 7, thus forcing the gripping edges into the metal. When a suflicient engagement has been secured, the screw will be turned out of the hole into which it is embedded and removed. For obvious reasons, an extractor with a left-hand thread will be used where a screw or pipe with a right hand thread is to be extracted, and vice versa.

Heretofore, when the extractor has been inserted into the previously prepared hole, the pressure of the helically disposed lands as they were forced into the article would have a considerable outward radial component due to the fact that the gripping edges had a negative rake, thus tending to expand unduly the hole in the object to be removed and to force the thread on the broken part into still tighter engagement with the surfaces retaining it. This tendency had to the effect of defeating the purpose of the operation since expansion of the hole lessens the grip of the tool on the broken part, and the outward pressure on the screw threads locked the part still more tightly in place. The present tool overcomes this objectionable tendency due to the fact that the gripping edge of the land or rib, as shown at 9 in Fig. 2, is radially disposed with an approximately zero rake, or overhanging with a positive rake, i. e., so that the surface corresponding to 12 in Fig. 2 slopes behind a radial line drawn to the gripping edge, and the lands grip the metal with little or no outward or radial component. Almost all the turning force is utilized in the tangential component thereof to unscrew the object to be removed. In extracting tools as previously made, the lands have been made with a negative rake, i. e., so that the surface corresponding to 12 in Fig. 2 sloped ahead of a radial line drawn to the gripping edge. The result of this was that the lands or ribs had a large outward or radial component and a small tangential component, thus forcing the gripping or cutting edges to expand the hole instead of unscrewing the object to be removed.

The modification of the extracting tool shown in Fig. 3 of the drawing operates on the same principle, the lands cutting their way into the broken part rather than being forced thereinto but, in addition, this modification is also provided with helically disposed ridges in the grooves or flutes 19 so as to support the gripping edges 21. These ridges 22 may be disposed directly behind the gripping edges so as to prevent breaking of the latter since the pressure on the lands is largely tangential due to the zero or positive rake placed on the gripping edges. The convexity upon the edges will thus tend to resist the shearing action ofthis tangential force while also preventing the lands from penetrating too deeply and thus expanding the provided hole.

The new cutting tool herein described having gripping edges with from approximately a zero rake to a positive rake, engages the metal of the part to be removed more eifectively, i. e., the force exerted has a greater tangential component than the old style tooth or land since the rake-shaped edge cuts into and grips the metalwithout expanding the hole and secures a maximum tangential turning moment which readily forces the, part out of its seat when the tool has been sufficiently inserted.

It will be apparent that changes may be made in the configuration of the tool and the number of lands or grooves, as well as their pitch, may be altered as desired for different uses without departing from the scope of the invention, it being intended to include any extracting tool with the gripping edges or teeth having approximately a zero rake or a positive rake.

Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the mechanism herein disclosed, provided the means stated by any of the following claims or the equivalent of such stated means be employed.

We therefore particularly point out and distinctly claim as our invention:

1. An extracting tool comprising an operating portion provided with helically disposed lands and grooves, said lands having gripping edges with at least zero rake, and said grooves having helically disposed ridges adjacent to said gripping edges to support said edges and to limit penetration of the lands thus preventing undue expansion of the hole provided for insertion of the tool.

2. An extracting tool comprising an operating portion, provided with helically disposed lands and grooves, said lands having gripping edges with a positive rake, and said grooves having helically disposed ridges directly behind said gripping edges, to support said edges and to limit the penetration of the lands preventing undue expansion of the hole provided for the insertion of the tool.

3. An extracting tool comprising a uniformly tapered operating portion provided with helically disposed lands and grooves, said lands having gripping edges with a positive rake and said grooves having helically disposed ridges directly behind said gripping edges to support said edges and to limit the penetration of the lands preventing undue expansion of the hole provided for the insertion of the extracting tool.

Signed by us this 29th day of June, 1931.

NORMAN RANDALL. JAMES B. DILLARD. 

